The present invention relates to a reflector for a light source lamp that is usable in a projecting device, such as a liquid crystal projector, an overhead projector or a motion picture projector, a lighting device for obtaining general illumination, spotlight or the like, or other devices.
As a mirror base member of a reflector for use in a projecting or lighting device, there has been used a glass member having, on its front side, a concave surface forming a paraboloid of revolution or an ellipsoid of revolution. On the concave surface of the mirror base member, a multilayer reflecting film (e.g. a multilayer film formed by stacking SiO2 films and TiO2 films alternately in 25 to 50 layers) is formed by sputtering or vacuum deposition. In this fashion, the reflector having a concave reflecting surface has been produced. Incidentally, a mounting hole is formed at the center of the mirror base member for mounting a light source lamp.
It is possible that the light source lamp bursts up due to an occurrence of stress concentration caused by long-term use or due to abnormal electric discharge. In view of this, the front side of the reflector is sealed by a protective glass plate. This prevents, even when the light source lamp bursts up, fragments of the broken lamp from flying forward.
Because such a projecting or lighting device requires strong visible light, an extra-high pressure mercury lamp, an arc metal halide lamp, a halogen lamp or the like has been used as the light source lamp. The light source lamp of this type radiates infrared light in addition to visible light, so that the mirror base member and protective glass plate of the reflector are heated.
Therefore, it is required that the mirror base member and protective glass plate of the reflector have excellent heat resistance and excellent heat/impact resistance. For the mirror base member of the reflector, low-expansive borosilicate glass or crystallized glass has been used, while low-expansive borosilicate glass has been used for the protective glass plate of the reflector. However, when heated over a long term, a stress is generated in the mirror base member so that even a slight impact causes cracks, leading to exfolication of the multilayer reflecting film, and according to circumstances, leading to breakage of the mirror base member.
In view of this, there has been proposed a reflector in JP-A-9-55109, wherein a plurality of radiation fins are provided on the back side of a mirror base member opposite from a concave surface thereof. However, providing the radiation fins on the outer surface of the mirror base member makes difficult the formation thereof, leading to low yield and increased cost.
If the light source lamp is designed to have higher intensity, i.e. higher wattage, to make a projected image brighter, the calorific value of the light source lamp increases following it. In this event, sufficient heat radiation can not be achieved only by providing the radiation fins on the back side of the mirror base member, thus leading to a possibility of generation of cracks and breakage of the mirror base member. Further, the internal pressure of the light source lamp increases and, following this, the frequency in bursts of such light source lamps increases and, simultaneously, the impact upon such burst also increases. As a result, it is possible that the conventional protective glass plate made of borosilicate glass is broken due to fragments upon burst of the light source lamp, and thus can not sufficiently function as the protective glass plate.
On the other hand, the thickness of the conventional protective glass plate is set to approximately 5 mm. In this regard, an attempt has been made to prevent the breakage of the protective glass plate by increasing the thickness thereof or by using a plurality of protective glass plates. However, these countermeasures increase the weight and size of the projecting or lighting device, and thus are not practical.
It is therefore an object of the present invention to provide a reflector that is excellent in heat resistance and can be produced at a low cost.
It is another object of the present invention to provide a reflector that is reluctant to generate a crack or breakage thereof even when heated over a long term by a light source lamp with a large calorific value.
Other objects of the present invention will become clear as the description proceeds.
According to an aspect of the present invention, there is provided a reflector which comprises a mirror base member having a concave surface, a reflecting film formed on the concave surface, and a protective glass plate attached to the mirror base member for preventing the fragments of the broken lamp from flying forward, at least one of the mirror base member and the protective glass plate being made of a glass member whose mechanical strength is enhanced.
According to another aspect of the present invention, there is provided a reflector which comprises a mirror base member having a concave surface and a reflecting film formed on the concave surface, the mirror base member being made of a glass member and having a back side which faces opposite the concave surface and is formed in a concavo-convex fashion.